Position detection apparatus and exposure apparatus

ABSTRACT

A position detection apparatus for detecting a position of a mark on an object includes a camera which captures an image of the mark, an extraction section which extracts a plurality of edge positions of the mark based on a signal derived from the image of the mark, each of the edge positions being associated with a combination of a direction and a polarity of the signal, and a determination section which determines a position of the mark, by comparing each of the plurality of extracted edge positions with a corresponding one of templates prepared for the respective combinations.

This application is a divisional application of patent application Ser.No. 09/521,210, filed on Mar. 8, 2000 now U.S. Pat. No. 6,925,203.

FIELD OF THE INVENTION

The present invention relates to a position detection apparatus fordetecting the position of a mark on an object and an exposure apparatususing the position detection apparatus.

BACKGROUND OF THE INVENTION

In an exposure apparatus for manufacturing, e.g., semiconductor devicesthat are increasingly shrinking in their feature sizes, before a reticlepattern is projected onto a wafer by exposure, the wafer and reticle arealigned.

Alignment includes two techniques: pre-alignment and fine alignment. Inpre-alignment, a feed shift amount generated when a wafer is loaded froma wafer conveyor apparatus onto a wafer chuck on a stage in asemiconductor exposure apparatus is detected, and the wafer is coarselyaligned within an accuracy with which subsequent fine alignment can benormally processed. In fine alignment, the position of the wafer placedon the wafer chuck on the stage is accurately measured, and the waferand reticle are precisely aligned such that the alignment error betweenthe wafer and reticle fall within the allowable range. The pre-alignmentaccuracy is, e.g., about 3 μm. The fine alignment accuracy is, e.g., 80nm or less for a 64 MDRAM although it changes depending on therequirement for wafer work accuracy.

Pre-alignment requires detection in a very wide range because the waferfeed shift generated when the conveyor apparatus feeds a wafer onto thechuck is detected, as described above. The detection range is generallyabout 500 μm square. As a method of detecting the X- and Y-coordinatesof one mark and performing pre-alignment, pattern matching is oftenused.

Pattern matching is roughly classified into two techniques. In onetechnique, a mark image is binarized, the binary image is matched with apredetermined template, and a position at which the binary image andtemplate have the highest correlation is determined as a mark position.In the other technique, the correlation between a mark image thatremains a grayscale image and a template having grayscale information iscalculated. As the latter method, normalization correlation is oftenused.

In pre-alignment, the mark to be used must be small although thedetection range is very wide. This is because as a pattern other than asemiconductor element is used as a mark, the mark is preferably as smallas possible to make the semiconductor element area as large as possible.Hence, the mark is often laid out in a region that is not used as anelement, e.g., on a scribing line. The mark size is therefore limited bythe scribing line width.

The scribing line width is becoming narrower year by year because of thehigh efficiency of semiconductor manufacturing and improved workaccuracy in recent years. Currently, the scribing line width is as smallas 100 μm or less, and accordingly, the mark size is also 60 μm or less.

On the other hand, to manufacture a semiconductor device with highdensity, a wafer is processed through new processes.

A problem associated with pre-alignment mark detection will be describedwith reference to FIGS. 6A to 6H. FIG. 6A shows a layout in which asemiconductor element pattern is adjacent outside a cross-shaped mark100, in which a portion “win” long in the horizontal direction is asignal detection region. FIGS. 6B and 6D show detection signalwaveforms, and FIGS. 6C and 6E show the wafer sectional structurescorresponding to the signals shown in FIGS. 6B and 6D. FIG. 6F alsoshows the cross-shaped detection mark 100. FIG. 6G shows the detectionsignal waveform. FIG. 6H shows the wafer section structure correspondingto FIG. 6G.

FIG. 6E shows the sectional structure of the mark after an ultra lowstep process. FIG. 6H shows the sectional structure of the mark after aCMP process. In these examples, it is difficult to detect thepre-alignment mark.

In pre-alignment, generally, a mark once formed is continuously used forposition detection even in the subsequent processes. However, as layersare deposited on the mark, it gradually becomes hard to observe themark. In the sectional structure shown in FIG. 6E, since a mark havinglow reflectivity and small step difference is present in a materialhaving high reflectivity and large step difference, the mark can hardlybe detected. In addition, since various layers are deposited on themark, the image obtained by reading the mark may have low contrast andmuch noise.

The examples shown in FIGS. 6A to 6H suggest that along with theprogress in techniques of manufacturing a semiconductor device with highdensity, processes that make detection of a pre-alignment mark presentin a wide detection range by the conventional pattern matching haveemerged and they present problems.

For example, a shown in FIG. 6E, when the mark has a small stepdifferences; although the peripheral pattern has a large step and highreflectivity, an image signal shown in FIG. 6D is obtained. The imagesignal shown in FIG. 6D is a signal in the region “win” shown in FIG.6A, which is obtained by sensing the pre-alignment mark 100 irradiatedby dark field illumination. The ordinate represents a video signalvoltage, and the abscissa represents a coordinate. When the signal isbinarized using a predetermined threshold value, the mark disappearsbecause the signal level of the mark portion is low. For this reason,the mark cannot be recognized by template matching.

Even with normalization correlation which is known as a detection methodfor a grayscale image, it is also difficult to detect a mark in an imagewith small step difference and low contrast or a noisy image.Especially, the detection rate of normalization correlation tends to below when the influence of noise is large, or mark defects occur in thewafer process. Additionally, the process time is long because of thecomplex calculation method.

Various approximation calculations have also been examined to solve theabove problem. However, the problem of a low detection rate for alow-contrast image remains unsolved.

Another well-known mark detection method is the vector correlationmethod (Video Information 1992/2). The vector correlation method canobtain a high detection rate even when the mark image has noise or themark has a defect. In the vector correlation method, attributeinformation representing the feature of edge information is extractedtogether with the edge of the mark. With this correlation calculationmethod, the extracted feature is compared with a template to detect themark position.

In the vector correlation method, a high-contrast mark and low-contrastmark cannot be detected using the same parameter in extracting the edgeinformation of the marks. Hence, the edge extraction parameter needs tobe tuned.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its object to stably detect the position of a markeven in a mark image that is difficult to detect, e.g., a low-contrastmark image, a noisy mark image, or a mark image whose mark has a defectgenerated in the wafer process. Especially in association with thevector correlation method, it is another object of the present inventionto optimize a mark detection method in accordance with a mark image inextracting information related to an edge and to stably detect the markposition and, more specifically, to cope with any mark image by selflearning and to stably detect the mark position.

According to the first aspect of the present invention, there isprovided a position detection apparatus for detecting a position of amark on an object, comprising an extraction section for observing themark and extracting a plurality of edge information data of the mark incorrespondence with attribute information representing features of theedge information, respectively, a position determination section forcomparing each edge information with one of a plurality of templates,which is specified by attribute information corresponding to the edgeinformation and evaluating a plurality of comparison results obtained bycomparison to determine the position of the mark, and a control sectionfor changing at least one of an extraction rule in the extractionsection and an evaluation rule in the position determination section onthe basis of the plurality of comparison results by the positiondetermination section and causing the extraction section and theposition determination section to execute processing again.

In the position detection apparatus according to the first aspect of thepresent invention, each attribute information data preferably representsan edge portion of the mark, which is associated with the correspondingedge information. In addition, each attribute information datapreferably represents one of a plurality of extraction conditions underwhich the corresponding edge information is extracted.

In the position detection apparatus according to the first aspect of thepresent invention, preferably, the extraction section extracts, as eachedge information data, information representing an edge position shiftedfrom an actual edge position of the mark by a predetermined distance inone of a plurality of predetermined directions, and each attributeinformation data represents a direction in which an edge positionassociated with the corresponding edge information is shifted from theactual edge position of the mark by the predetermined distance.

In the position detection apparatus according to the first aspect of thepresent invention, the extraction section preferably comprises an imagesensing section for sensing an image of the mark, a differentialprocessing section for differentiating the mark image as an imagesensing result, and an edge information generation section forprocessing the differential result to generate the edge informationcorresponding to the attribute information.

Preferably, the differential processing section calculates a change rateof an image signal of the mark image along at least two directions ofthe mark image, and each attribute information data is associated withone of the at least two directions.

Alternatively, each attribute information data is preferably associatedwith a sign of the differential result by the differential processingsection.

Alternatively, preferably, the differential processing sectioncalculates a change rate of an image signal of the mark image across themark image along row and column directions of the mark image, and eachattribute information data is associated with one of the row and columndirections and the differential result by the differential processingsection.

In the position detection apparatus according to the first aspect of thepresent invention, each template preferably includes, as information tobe compared with the edge information, position information of aplurality of points defining a corresponding edge.

In the position detection apparatus according to the first aspect of thepresent invention, the extraction section preferably performs noiseremoval processing for an observation result of the mark and thenexecutes edge information extraction.

In the position detection apparatus according to the first aspect of thepresent invention, the extraction section preferably increases a linewidth associated with the extracted edge information.

In the position detection apparatus according to the first aspect of thepresent invention, the extraction rule and/or the evaluation ruledetermined by the control section is preferably stored in a memory andused as a base for processing to be executed later.

In the position detection apparatus according to the first aspect of thepresent invention, the extraction section preferably observes the markunder dark field illumination.

According to the second aspect of the present invention, there isprovided a position detection apparatus for detecting a position of amark on an object, comprising an extraction section for observing themark and extracting edge information of the mark, a positiondetermination section for comparing the edge information with a templateand evaluating a comparison result to determine the position of themark, and a control section for changing at least one of an extractionrule in the extraction section and an evaluation rule in the positiondetermination section on the basis of the evaluation result by theposition determination section and causing the extraction section andthe position determination section to execute processing again.

According to the third aspect of the present invention, there isprovided an exposure apparatus comprising a projection optical systemfor projecting a pattern onto a substrate, a chuck on which thesubstrate is placed, and a position detection section for detecting aposition of a mark on the substrate placed on the chuck, wherein thesubstrate is aligned on the basis of a detection result by the positiondetection section, and then, the substrate is exposed using the pattern,and position detection section comprising an extraction section forobserving the mark and extracting a plurality of edge information dataof the mark in correspondence with attribute information representingfeatures of the edge information, respectively, a position determinationsection for comparing each edge information data with one of a pluralityof templates, which is specified by attribute information correspondingto the edge information and evaluating a plurality of comparison resultsobtained by comparison to determine the position of the mark, and acontrol section for changing at least one of an extraction rule in theextraction section and an evaluation rule in the position determinationsection on the basis of the plurality of comparison results by theposition determination section and causing the extraction section andthe position determination section to execute processing again.

In the exposure apparatus according to the third aspect of the presentinvention, the extraction section of the position detection sectionpreferably observes the mark with an off-axis scope or TTR (Through TheReticle) or TTL (Through The Lens).

According to the fourth aspect of the present invention, there isprovided an exposure apparatus comprising a projection optical systemfor projecting a pattern onto a substrate, a chuck on which thesubstrate is placed, and a position detection section for detecting aposition of a mark on the substrate placed on the chuck, wherein thesubstrate is aligned on the basis of a detection result by the positiondetection section, and then, the substrate is exposed using the pattern,the position detection section comprising an extraction section forobserving the mark and extracting edge information of the mark, aposition determination section for comparing the edge information with atemplate and evaluating a comparison result to determine the position ofthe mark, and a control section for changing at least one of anextraction rule in the extraction section and an evaluation rule in theposition determination section on the basis of the evaluation result bythe position determination section and causing the extraction sectionand the position determination section to execute processing again.

According to the fifth aspect of the present invention, there isprovided a position detection method of detecting a position of a markon an object, comprising the extraction step of observing the mark andextracting a plurality of edge information data of the mark incorrespondence with attribute information representing features of theedge information, respectively, the position determination step ofcomparing each edge information data with one of a plurality oftemplates, which is specified by attribute information corresponding tothe edge information and evaluating a plurality of comparison resultsobtained by comparison to determine the position of the mark, and thecontrol step of changing at least one of an extraction rule in theextraction step and an evaluation rule in the position determinationstep on the basis of the plurality of comparison results in the positiondetermination step and causing the extraction step and the positiondetermination step to execute processing again.

According to the sixth aspect of the present invention, there isprovided a position detection method of detecting a position of a markon an object, comprising the extraction step of observing the mark andextracting edge information of the mark, the position determination stepof comparing the edge information with a template and evaluating acomparison result to determine the position of the mark, and the controlstep of changing at least one of an extraction rule in the extractionstep and an evaluation rule in the position determination step on thebasis of the evaluation result in the position determination step andcausing the extraction step and the position determination step toexecute processing again.

Further objects, features and advantages of the present invention willbecome apparent from the following detailed description of theembodiments of the present invention with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of image processing in an exposure apparatusaccording to a preferred embodiment of the present invention;

FIGS. 2A to 2C are schematic views of exposure apparatuses according topreferred embodiments;

FIG. 3 is a view for explaining mark edge extraction processing in thepreferred embodiment of the present invention;

FIG. 4A is a view showing synthesized edge portions extracted from apre-alignment mark image;

FIGS. 4B to 4E are views showing edge components (edge information)extracted from the pre-alignment mark image;

FIG. 5A is a view showing synthesized templates according to thepreferred embodiment of the present invention;

FIGS. 5B to 5E are views showing templates according to the preferredembodiment of the present invention; and

FIGS. 6A to 6H are views showing pre-alignment marks and their stepdifferences and video signals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2A is a view showing the schematic arrangement of a semiconductorexposure apparatus according to a preferred embodiment of the presentinvention. In this exposure apparatus, a mark for pre-alignment isdetected using an off-axis scope 6.

A pattern for exposure is formed on a reticle 1. The pattern isilluminated with, e.g., an i-line or excimer laser light source of anillumination system (not shown) and projected onto a wafer 5 through aprojecting lens 2.

Pre-alignment is performed after the wafer 5 is placed on a wafer chuck4 on an X-Y stage 3 by a wafer conveyor apparatus (not shown). Since thewafer 5 is placed on the wafer chuck 4 at the accuracy depending on theconveyor apparatus, the alignment accuracy is low. Hence, accurate waferposition measurement cannot be directly started. To do this, apre-alignment (coarse alignment) mark on the wafer is observed with theoff-axis scope 6 arranged outside the projecting lens 2, the opticalimage of the mark is photoelectrically converted by a CCD camera 7, andthen the position information of the mark is detected by a pre-alignmentimage processing unit 8. In the pre-alignment image processing unit 8,the photoelectrically converted video signal is converted into digitalinformation by an A/D conversion unit 71, and the pre-alignment markposition is detected by an image processor 72 having an image memory.

It is advantageous when both the X- and Y-coordinates can be detected byone mark. For this reason, the pre-alignment mark has the same shape asthat of the mark 100 shown in FIG. 6A. The position of the X-Y stage 3when the pre-alignment mark image is caputured is accurately measured bya laser interferometer 12. On the basis of the mark position shift andthe position of the X-Y stage 3, a controller 9 accurately measures theshift amount of the wafer 5 placed on the chuck 4. The X-Y stage 3 isdriven by a stage driving unit 13.

In this embodiment, a case wherein dark field illumination is employedas illumination for the off-axis scope 6 will be described. In darkfield illumination, scattered light from an edge position of the markstep difference is received by the CCD camera 7. The present inventioncan also be applied to bright field illumination.

FIG. 1 shows the flow of image processing (position detectionprocessing) for executing pre-alignment in a position detectionapparatus according to the preferred embodiment of the present inventionand a semiconductor exposure apparatus using the position detectionapparatus.

First, the vector correlation method (S100, S101, S102) will bedescribed.

In step S100, the image processor 72 executes edge extraction processingfor an image captured by the CCD camera 7. In edge extractionprocessing, both the edge information of the mark image and attributeinformation representing that the edge information is associated withthe upper, lower, right, or left side of the mark image aresimultaneously acquired.

In this embodiment, edge information (solid lines in FIGS. 4B to 4E) aremade to correspond to attribute information (“over”, “under”, “left”,and “right” in FIGS. 4B to 4E) and extracted for four directions of theupper, lower, left, and right sides of an actual edge of the mark image.Edge information may be made to correspond to attribute information andacquired not only for the four directions of the upper, lower, left, andright sides of an actual edge but also for, e.g., four directions thatrespectively make an angle of 45° with the above four directions, i.e.,a total of eight directions. Alternatively, edge information may be madeto correspond to attribute information and acquired according to anotherrule.

In step S101, the mark image is searched on the basis of edgeinformation and attribute information corresponding to the edgeinformation. Searching means detection of an approximate position of themark image. In searching the mark image, the degree of matching betweenthe edge information extracted in step S100 and a template specified bythe attribute information corresponding to the edge information isoccasionally calculated while moving the template within a predeterminedregion, and the center coordinates of the mark (center coordinates ofthe template) at which the maximum degree of matching is obtained aredetermined. Each template is formed from feature points of interestcorresponding to attribute information, to which attention must be paidin comparison with the edge information extracted from the mark image.

To calculate the degree of matching, the edge information (e.g., FIG.4B) extracted in step S100 is compared to corresponding feature pointsof interest (e.g., FIG. 5B) in the template to determine whether the twopieces of information match, and the comparison results are evaluated.More specifically, the degree of matching is calculated by comparing theedge information shown in FIG. 4B with the feature points of interest ofthe template shown in FIG. 5B, the edge information shown in FIG. 4Cwith the feature points of interest of the template shown in FIG. 5C,the edge information shown in FIG. 4D with the feature points ofinterest of the template shown in FIG. 5D, and the edge informationshown in FIG. 4E with the feature points of interest of the templateshown in FIG. 5E while changing the center coordinates (position of +)and evaluating the number of matches obtained. The center coordinates ofa template, at which the maximum degree of matching is obtained, isdetected as the position of the mark image.

It is determined in step S102 whether the mark position search issuccessful. More specifically, when the matching result (maximum degreeof matching) has a value equal to or larger than a threshold value fordetection determination, it is determined that mark position detectionis successful, and the position of the mark is precisely measured instep S103.

Mark position search fails in step S102 when 1) the matching result(maximum degree of matching) has a value smaller than the thresholdvalue for detection determination or 2) a degree of matching equal to orhigher than the level of threshold value for detection determination isobtained at a plurality of mark positions, and one of them cannot beselected.

Processing of a characteristic feature of the present invention startsfrom step S104.

If mark position search fails, the flow advances the loop including stepS104 to change parameters for detection, i.e., to adjust one or both ofthe edge extraction processing parameter and the threshold value fordetection determination, and edge extraction (S100), mark positionsearch (S101), and detection determination (S102) are performed again.The repetitive loop of parameter change and search is controlled on thebasis of the number of times or conditions set in advance. If it isdetermined that the mark position cannot be accurately detected any moreeven by repeating the repetitive loop, a detection error occurs.

Actual processing according to the flow will be described next withreference to FIGS. 3 and 4A to 4E. First, vector correlation will bedescribed. In edge extraction in step S100, scattered light from themark 100 is received and photoelectrically converted by the CCD camera7, then A/D-converted by the A/D conversion unit 71, and stored in theimage memory of the processor 72.

An image signal along a given scanning line (row) of the stored image isrepresented by Xi. Since this embodiment employs dark fieldillumination, the image signal Xi has a certain value at the mark edgeposition and a value of black level at the remaining portions. A signalobtained by differentiating the image signal Xi is a differential signalXid. When the scanning line is traced from the left to the right, thedifferential signal Xid becomes positive at the leading edge portion ofthe image signal Xi and negative at the trailing edge portion.

A threshold value thl is set on the positive side of the differentialsignal Xid. When the differential signal Xid is binarized using thethreshold value thl as a reference, a left edge signal Le is obtained.In a similar way, when a threshold value thr is set on the negative sideof the differential signal Xid, and the signal Xid is binarized usingthe threshold value thr as a reference, a right edge signal Re isobtained. The left edge signal Le represents the left edge position ofthe mark image, and the right edge signal Re represents the right edgeposition of the mark image. When the above processing is executed forall scanning lines, pieces of edge information representing the leftedge positions of the mark image and pieces of edge informationrepresenting the right edge positions are obtained.

An image signal along a vertical line (column) on the image memory isrepresented by Yi. Like the image signal Xi, the image signal Yi istraced from the lower side to the upper side, and a differential signalYid is generated. When the differential signal Yid is binarized usingthreshold values thu and tho, an under edge signal Ue and over edgesignal Oe are obtained. The under edge signal Ue represents the underedge position of the mark image, and the over edge signal Oe representsthe over edge position of the mark image. When the above processing isexecuted for all vertical lines, pieces of edge information representingthe under edge positions of the mark image and pieces of edgeinformation representing the over edge positions are obtained.

In FIG. 4A, edge information representing the right edge positions, edgeinformation representing the left edge positions, edge informationrepresenting the over edge positions, and edge information representingthe under edge positions all of the mark 100 are synthesized andtwo-dimensionally illustrated. In this embodiment, as edge positionimages (edge information and attribute information), edge informationassociated with attribute information “over” shown in FIG. 4B, edgeinformation associated with attribute information “under” shown in FIG.4C, edge information associated with attribute information “left” shownin FIG. 4D, edge information associated with attribute information“right” shown in FIG. 4E are stored in the processor 72 as independentinformation.

Mark image search (S101) is performed by matching calculation oftemplates stored in advance and edge position images (edge information)shown in FIGS. 4B to 4E.

FIGS. 5A to 5E are views for explaining the templates.

Since the positions of the over, under, left, and right edges relativeto the mark center (cross) are known, the templates are registered aslayouts shown in FIGS. 5B to 5E in which feature portions of the markare indicated by open circles. That is, the templates can be determinedon the basis of the shape of the mark to be formed on the wafer. FIG. 5Ashows the synthesized image of the four registered templates shown inFIGS. 5B to 5E. In this embodiment, the position of an open circle iscalled a feature point of interest, and a set of points of interest iscalled a template. In each template of this embodiment, feature pointsof interest are defined on only one side edges of the mark. For example,in the template shown in FIG. 5B, the feature points of interest aredefined on only the over edges of the mark.

Matching calculation in a mark image search is performed by determiningwhether, e.g., the pieces of edge information shown in FIG. 4B arepresent at the positions of open circles in FIG. 5B with reference tothe mark center (cross). In a similar way, FIG. 4C and FIG. 5C, FIG. 4Dand FIG. 5D, FIG. 4E and FIG. 5E are compared to determine whether thepieces of edge information shown in FIGS. 4C to 4E are present at theposition of open circles in FIGS. 5C to 5E, respectively. When the edgeinformation are present at all the hollow bullet positions, the degreeof matching is 100%. If some hollow bullet positions have no edgeinformation, the degree of matching is lower than 100%. The abovematching calculation is performed for the entire edge images whilechanging the mark center coordinates, and mark center coordinates atwhich the degree of matching is highest are finally extracted, therebycompleting the search.

The feature points of interest shown in FIGS. 5B to 5E are defined bythinning out points and designating two points that define specificedges. Even when the number of feature points of interest is increased,no effect is obtained unless they express the characteristic feature ofthe mark shape. If the feature points of interest are densely defined,the degree of matching becomes low due to various reasons, and the markimage may not be detected. Especially, when the mark is damaged, thedegree of matching often extremely lowers. For this reason, a highdetection rate can be stably obtained by setting thinned out featurepoints of interest, as described above.

Vector correlation has been described above.

When the maximum degree of matching obtained by the above-describedsearch is lower than the level of threshold value for determination, thecoordinates at which the maximum degree of matching is obtained may notindicate the correct mark position. In this case, edge informationextraction may not be optimum. Hence, preferably, the threshold valuesthl, thr, thu, and tho used for extraction of mark edge information arecorrected, the edge information data are generated again; and the searchis repeated.

For example, when the threshold values thl, thr, thu, and tho for edgeinformation is obtained from a low-contrast mark image. Hence, thedegree of matching in the search is low, and mark detectiondetermination is impossible. Preferably, the edge information of themark is detected while gradually decreasing the threshold value for edgeextraction. This makes it possible to obtain a sufficient degree ofmatching in the search.

As another example, when there are a plurality of coordinates at which adegree of matching higher than the level of threshold value fordetermination, the mark position cannot be determined. In this case aswell, the mark position can be reliably determined by increasing thedetermination threshold value and repeating edge information generationand search.

The position detection parameter such as the threshold value for edgeextraction or threshold value for determination can be efficientlychanged by storing, e.g., a value determined according to theimmediately preceding search processing result (degree of matching) inthe memory and using the value as the base (e.g., initial value) fordetection parameter determination of the next time.

For precise detection (S103) after the end of the mark image search, themark position can be determined at an accuracy beyond the pixelresolution by, e.g., a method of obtaining the barycenter on the basisof the luminance distribution with an origin set at the centercoordinates of the M/D-converted image found by the search.

In this embodiment, edge extraction is performed immediately after imagereception. Processing of performing noise removal filtering before edgeextraction to lower the noise level in advance and prevent anyunnecessary edge information, or forming a bold line image as edgeinformation to correct deformation in mark size or omission of edges isalso effective. Addition of the above processing results in an increasein detection rate in the mark search.

In the first embodiment, the position detection apparatus of the presentinvention and the semiconductor exposure apparatus using the positiondetection apparatus are applied to pre-alignment using the off-axisscope 6. However, the process of the mark position search is not limitedto pre-alignment using off-axis.

FIG. 2B shows the second embodiment in which the position detectionapparatus of the present invention is applied to a TTR detection systemfor detecting a mark on a wafer 5 or stage through a reticle 1 in asemiconductor exposure apparatus.

To detect a mark in the TTR detection system, exposure light is used.For example, in a semiconductor exposure apparatus using an excimerlaser, a CCD camera 7 and laser 21 are synchronized by a sync signalgenerator 20 to emit a laser beam only during the light storage time ofthe CCD camera 7. For the photoelectrically converted mark image, themark position search is done by the same method as in the firstembodiment, and after the search, an accurate mark position can becalculated. In an i-line exposure apparatus, since the light source isnot a laser, synchronization between image reception and theillumination system is unnecessary. For this reason, the mark positionsearch can be done, and accurate mark position calculation can beperformed after the search, as in the first embodiment.

In reticle alignment for alignment of the reticle 1 with respect to aprojecting lens 2 as well, the same processing as in the firstembodiment can be performed for a mark search.

FIG. 2C shows the third embodiment of the present invention in which theposition detection apparatus of the present invention is applied to aTTL detection system for detecting the mark position on a wafer 5 orstage 3 through a projecting lens 2 without interposing a reticle 1 in asemiconductor exposure apparatus. In TTL as well, the mark search andposition determination can be performed by the same method as that ofthe first embodiment except that the mark image sensing method isdifferent.

As has been described above, in the position detection apparatusaccording to the preferred embodiment of the present invention and thesemiconductor exposure apparatus using the position detection apparatus,the edge information of a mark image is extracted in correspondence withattribute information, the edge information is compared with acorresponding template in units of partial edges on the basis of theattribute information, and the obtained comparison result is evaluated,thereby determining the mark position. Since it can be determined athigh probability in units of partial edges whether a partial edge (e.g.,FIG. 4B) and a template (e.g., FIG. 5B) corresponding to the edge match,the probability of mark position detection becomes higher than that ofthe prior art in which it is determined whether the entire mark imagematches the template. Hence, according to this embodiment, the positionof the image of a mark with degradation or a defect generated inmanufacturing a high-density semiconductor device, e.g., a low-contrastmark image, a noisy mark image, or a mark image obtained by sensing adefect generated in the wafer process can be more stably detected.

As a consequence, in this position detection apparatus and semiconductorexposure apparatus using the position detection apparatus, by repeatingpattern matching while adjusting one or both of the edge extractionparameter and parameter used to determine the matching result inaccordance with the result of template matching, the image of a markwith degradation or a defect can be more reliably detected.

The present invention is not limited to the above embodiments andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore, to apprise the public of thescope of the present invention, the following claims are made.

1. An exposure apparatus comprising: a projection optical system forprojecting a pattern onto a substrate; a chuck on which the substrate isplaced; and a position detection section for detecting a position of amark on the substrate placed on said chuck, wherein the substrate isaligned on the basis of a detection result by said position detectionsection, and then, the substrate is exposed using the pattern, saidposition detection section comprising: an extraction section forobserving the mark and extracting a plurality of edge information of themark in correspondence with attribute information representing featuresof the edge information, respectively; a position determination sectionfor comparing each edge information with one of a plurality oftemplates, which is specified by attribute information corresponding tothe edge information and evaluating a plurality of comparison resultsobtained by comparison to determine the position of the mark; and acontrol section for changing at least one of an extraction rule in saidextraction section and an evaluation rule in said position determinationsection on the basis of the plurality of comparison results by saidposition determination section and causing said extraction section andsaid position determination section to execute processing again.
 2. Theapparatus according to claim 1, wherein said extraction section of saidposition detection section observes the mark with an off-axis scope. 3.The apparatus according to claim 1, wherein said extraction section ofsaid position detection section observes the mark by TTR (Through TheReticle).
 4. The apparatus according to claim 1, wherein said extractionsection of said position detection section observes the mark by TTL(Through The Lens).
 5. The apparatus according to claim 1, wherein eachattribute information represents an edge portion of the mark, which isassociated with the corresponding edge information.
 6. The apparatusaccording to claim 1, wherein each attribute information represents oneof a plurality of extraction conditions under which the correspondingedge information is extracted.
 7. The apparatus according to claim 1,wherein said extraction section extracts, as each edge information,information representing an edge position shifted from an actual edgeposition of the mark by a predetermined distance in one of a pluralityof predetermined directions, and each attribute information represents adirection in which an edge position associated with the correspondingedge information is shifted from the actual edge position of the mark bythe predetermined distance.
 8. The apparatus according to claim 1,wherein said extraction section comprises: an image sensing section forsensing an image of the mark; a differential processing section fordifferentiating the mark image as an image sensing result; and an edgeinformation generation section for processing the differential result togenerate the edge information corresponding to the attributeinformation.
 9. The apparatus according to claim 8, wherein saiddifferential processing section calculates a change rate of an imagesignal of the mark image along at least two directions of the markimage, and each attribute information is associated with one of the atleast two directions.
 10. The apparatus according to claim 9, whereineach attribute information is associated with a sign of the differentialresult by said differential processing section.
 11. The apparatusaccording to claim 8, wherein each attribute information is associatedwith a sign of the differential result by said differential processingsection.
 12. The apparatus according to claim 8, wherein saiddifferential processing section calculates a change rate of an imagesignal of the mark image across the mark image along row and columndirections of the mark image, and each attribute information isassociated with one of the row and column directions and thedifferential result by said differential processing section.
 13. Theapparatus according to claim 1, wherein each template includes, asinformation to be compared with the edge information, positioninformation of a plurality of points defining a corresponding edge. 14.The apparatus according to claim 1, wherein each template includes, asinformation to be compared with the edge information, positioninformation of points on a continuous line defining a correspondingedge.
 15. The apparatus according to claim 1, wherein said extractionsection performs noise removal processing for an observation result ofthe mark and then executes edge information extraction.
 16. Theapparatus according to claim 1, wherein said extraction sectionincreases a line width associated with the extracted edge information.17. The apparatus according to claim 1, wherein at least one of theextraction rule and the evaluation rule determined by said controlsection is stored in a memory and used as a base for processing to beexecuted later.
 18. The apparatus according to claim 1, wherein saidextraction section observes the mark under dark field illumination. 19.An exposure apparatus comprising: a projection optical system forprojecting a pattern onto a substrate; a chuck on which the substrate isplaced; and a position detection section for detecting a position of amark on the substrate placed on said chuck, wherein the substrate isaligned on the basis of a detection result by said position detectionsection, and then, the substrate is exposed using the pattern, saidposition detection section comprising: an extraction section forobserving the mark and extracting edge information of the mark; aposition determination section for comparing the edge information with atemplate and evaluating a comparison result to determine the position ofthe mark; and a control section for changing at least one of anextraction rule in said extraction section and an evaluation rule insaid position determination section on the basis of the evaluationresult by said position determination section and causing saidextraction section and said position determination section to executeprocessing again.